Hi

I have the following formula:
=LOOKUP(L7,{0,15,15.1,15.4,15.5,15.9,16,16.9,17,17 .9,18,18.9,19,19.9,20,20.9,21,21.9,22,22.9,23,23.9 ,24,24.9,25.0259},{"1.00","1.00","2.50","2.50","4. 00","4.00","5.50","5.50","6.50","6.50","7.00","7.0 0","8.75","8.75","9.50","9.50","10.75","10.75","12 .00","12.00","13.25","13.25","14.50""14.50","15.75 ","15.75"})

So the result of this lookup operation may be:

L7=2.50
L8=9.50
L9=13.25
and so on down to L650

Now I need to take this initial look up result and say if:
L7=1.00 return 0.00
if 2.50 return 1.75
if 4.00 return 3.50
if 5.50 return £4.50
and so on with 13 possible answers.

I have tried to do this using a further look-up formula, but it just returns
#NA! even when the L7 or L8 etc. is populated. Does anyone know how I get
round this?
Many thanks for any help.
Regards Liz